The half-bridge driver circuit is widely applied in the fields of motor drive, electronic ballast, switching power supply, etc., and is used for driving two power switch devices connected in a totem-pole manner to make the two power switch devices be alternately conducted. As shown in FIG. 1, a conventional half-bridge driver chip comprises a low-side channel logic circuit and a high-side channel logic circuit, wherein the low-side channel logic circuit comprises a low-side signal input circuit, a low-side delay circuit and a low-side signal output circuit; the high-side channel logic circuit comprise a high-side signal input circuit, a narrow pulse generation circuit, a high-voltage level shift circuit and a high-side channel high-basin logic circuit; the high-voltage level shift circuit which is used as an interface circuit of circuits in a high-voltage area and a low-voltage area (located at the edge of an isolation structure, and needing to work at several hundred volts) is composed of high-voltage power switch devices (M01 and M02), resistive loads (RL1 and RL2) and Zener clamping diodes (D01 and D02); the high-side channel high-basin logic circuit is located in a high-voltage circuit area and is powered by the high-side floating power supply VB, other circuits are located at a low-voltage circuit area and are powered by a low-side fixed power supply VCC, and both the circuits in the low-voltage area and the high-voltage area work under a voltage ranging from 10V to 20V. In order to increase the utilization efficiency of the power supply, the half-bridge driver chip is powered by a single power supply, wherein the low-voltage area is directly powered by a direct current power supply VCC, while the high-voltage area is in a floating state, and is powered by an external bootstrap capacitor. When a lower tube (low-side tube) ML in the half-bridge structure is switched on, and a higher tube (high-side tube) MH is switched off, the voltage of the high-side floating power supply VB drops with the voltage drop of a high-side floating ground VS, when the voltage of the VB drops below the voltage of the VCC, and the differential voltage between the two exceeds the turning-on voltage drop of a high-voltage bootstrap diode DB, the VCC charges the bootstrap capacitor CB through the bootstrap diode DB; when the higher tube is switched on and the lower tube is switched off, the voltage of the VB increases with the voltage increasing of the VS, the voltage of the VB far exceeds the voltage of the VCC, and the bootstrap diode DB is switched off, and the high-basin circuit is powered by the bootstrap capacitor CB.
The conventional half-bridge driver circuit with an external bootstrap diode DB has obviously defects: the externally arranged discrete device (bootstrap diode DB) will increase additional costs of the circuit, and will increase the system complexity; the high-voltage bootstrap diode has a higher turning-on voltage drop, which will finally affect the charging voltage on the capacitor CB; moreover, the higher the withstand voltage of the diode is, the larger the turning-on voltage drop is; and the reverse recovery current of the bootstrap diode DB will cause electric leakage of the bootstrap capacitor.
In order to realize the integration of the bootstrap diode, a BCD (Bipolar CMOS DMOS) technology can be used to integrate the high-voltage bootstrap diode into the half-bridge driver chip, but the high-voltage bootstrap diode made by this technology has larger leakage and will bring about very large leakage that affects the system reliability, and meanwhile, the charging efficiency of the bootstrap capacitor is decreased. An SOI (Silicon On Insulator) technology can also be used to integrate the high-voltage bootstrap diode into the half-bridge driver chip, but the half-bridge driver chip made by the SOI technology will greatly increase the cost of the chip and reduce the competitiveness of the product.
Therefore, U.S. Pat. No. 7,215,189B proposes a bootstrap diode emulator circuit with dynamic back-gate biasing, as shown in FIG. 2, to replace the bootstrap diode DB in FIG. 1. The bootstrap diode emulator circuit in the patent comprises a high-voltage power switch device LDMOS and a control circuit; an integrated high-voltage power switch device LDMOS is turned on and off to stimulate the positive turning-on and reverse turning-off functions of a bootstrap diode DB; when a low-side output LO is at a high level, the LDMOS is turned on, and a low-side fixed power supply VCC charges a bootstrap capacitor CB through the LDMOS, and when the low-side output LO is at a low level, the LDMOS is turned off, and the low-side fixed power supply VCC stops charging the bootstrap capacitor CB. However, this technology has the defect of low charging efficiency. To this end, U.S. Pat. No. 7,456,658B2 proposes an improved solution: a voltage comparator circuit is added for a VCC and a VB; when the high-side output and the low-side output are at a low level at the same time, the comparator is enabled, and the LDMOS is turned on in the case that the voltage value of the VB is smaller than a certain value, and the VCC charges the bootstrap capacitor. However, the high-voltage power switch device LDMOS and the control circuit added in the bootstrap diode emulator circuit adopted by the patent greatly increase the complexity of the circuit, and the area of the chip is greatly increased; moreover, the cost is also increased; moreover, compared with the diode, the on-resistance of the LDMOS device is relatively large, which seriously reduces the charging speed of the bootstrap circuit, so that the technical solution is not suitable for some applications, such as a high-frequency half-bridge driver circuit.